[EXTRACTED FROM THE REPORT OE t\iE U. S. COMMTSSTONEK OE EiSH AND FISHERIES FOR 1889 TO 1S;)1. Pages 5i« to Gil.] PLANKTONIC STUDIES: A COMPAIUTIVE INVESTIGATION OF THE IMPORTANCE AND CONSriTLlTION OF THE PELAGIC FAUNA AND FLORA. BY EHISTST II.ZECi4l. [TJa^NSriATED I3Y GEORGE WILX0:N^ EIELD.] washingto:n': GOVERNMENT PRINTING OFFICE. 1893. G-PLANKTOMC STUDIES: A COMPARATIVE INVESTIGATION OF THE IMPORTANCE xVND CONSTITUTION OF THE PELAGIC FAUNA AND FLORA. By Ernst H.eckel. [Trauslated hy George Wilton Field.] TRANSLATOR'S PREFACE. Prof. Haeckers " Plankton Stiulien " first appeared in the Jenaische Zeitschrift., vol. XXV, first and second parts, 1890. It was immediately published in separate form by Gustav Fischer, of Jena, and attracted much attention on the Continent and in England. The subject, "a comi)arative study of the importance and constitution of the marine fauna and flora," is presented in Prof. HiTeckel's usual pleasino- style, and the work can not fail to be of value to all interested in the bio- logical sciences, to the general reader as well as to the specialist. It derives especial interest in connection with the work of the Fish Com- mission, from its broad discussion of those many important elements which enter into the food supply of all pelagic fishes, such as the mackerel and menhaden, and, considering the extensive physical inves- tigations now being conducted in our coast waters by the schooner Granipiis, its publication at the present time will prove exceedingly advantageous. The terminology used by Prof. Haeckel may at first seem formidable, but this difficulty is more fancied than real. The ^terms are formed upon correct analogies, and most of them will probably find a perma- nent place. The definite restriction of the meaning of terms is a funda- mental necessity in every science, and for the lack of this the branch of biology here considered is in a very unsatisfactory condition. The author, first of all, proposes certain terms with a definite meaning. The word "plankton," from the Greek -Xayxro^, wandering, roaming, was, I believe, first employed by Hensen in j^lace of the German "Auftrieb," to designate all plants and animals found at the surface of the ocean which are carried about involuntarily in the water. Hteckel adopts this term, but objects somewhat to the meaning at present attached to it. Particularly valuable for us is the general review which the author gives of the discovery and growth of our knowledge of this branch, 565 566 REPORT OF COMMISSIONER OF FISH AND FISHERIES. which lie names "planktology"; the distinctions which he points out between the varied constituents and distribution of the plankton; and finally his extremely valuable suggestions for further work in the field which he so justly terms "a wonder-land." In the translation .the liberty of omitting a few personal references was taken, for the reason that we in this country know very little of the facts which have called them forth. In the case of several German words it has been found necessary for the sake of clearness to use a circumlocution. For instance, I can recall no English equivalent for '' Sioffwechsel des Meeres,^'' which would con- vey its meaning in a single word. The " cycle of matter in the sea," i. e., the change of inorganic matter into vegetable and animal organic matter, and this finally again into inorganic matter, seemed the best rendering, though even this does not include all which the German term implies. I.—HISTORICAL EXPLANATIONS. For the great progress made in the last half century in our knowledge of organic life, we are indebted—next to the theory of development—in a great measure to the investigation of the so-called " pelagic animal world." These wonderful organisms, which live and swim at the surface of the sea and at various depths, have long aroused the interest of sea farer and naturalist, by the wealth of the manifold and strange forms, as well as by the astonishing number of individuals—these have been referred to in many old as well as in recent narratives. A considerable number of these, especially of the larger and more remarkable forms, were described and figured in the last, or in the first half of the present, century. The new and comprehensive investigation of the "pelagic world" began in the fifth decade of our century, and is therefore not yet 50 years old. Into this, as into so many other regions of biology, the great Johannes Miiller, of Berlin, equally distinguished in the realms of morphology and physiology, entered as a pioneer. He was the first who systematically and with great results carried on the "pelagic fishery by means of a fine net." In the autunui of 1845, at Helgoland, he began his celebrated investigations upon the development of echinoderms, and obtained the small pelagic larvre of the echinoderms, and other small pelagic animals living with them, as sagitta, worm larvje, etc., at first by "microscopical examination of the sea water, which was brought in" (1). This wearisome and thankless method was soon displaced by the successful use of the "fine pelagic net." In the treatise "on the general plan in the development of the echinoderms," Note.—Citations inclosed in parentheses which occur in the text refer to the list of publications at the end of this paper (pp. 040, 641). : PLANKTONIC STUDIES. ^ 567 Miiller compares the different methods of obtaining- them, and chooses, above all, ''fishing- with a fine net at the snrface of the sea." He says I liave used this method for many years witli the best results; for the advanced stages of the swimming hirva^. and for the time of maturity and metamorphosis it is quite indis})ensable, and in no way to be repLaced. The students who, in 1845-46, as well as in the following years, accompanied Johannes Miiller to Helgoland and Trieste (Max Miiller, Busch, Wilms, Wagener, and others) were introduced into this method of "pelagic fishery'' and into the investigation of "pelagic tow-stuff" {pelddische Aii/trieh) obtained thereby. It was soon employed at sea with excellent results by other zoologists—by T. H. Huxley, by Krolm, Leuckart, Carl Vogt, and others, and especially by the three Wiirts- burg naturalists, A. Kolliker, Heinrich Miiller, and (3. Gegenbaur, who in 1852 examined with such brilliant success the treasures of the Straits of Messina. At this time, in the beginning of the second half of our century, the astonishing wealth of interesting- and instructive forms of life which the surface of the sea offers to the naturalist first became known, and that long series of important discoveries began which in the last forty years have filled so many volumes of our rapidly increasing zoological literature. A new and inexhaustibly rich field was thus opened to zootomical and microscopical investigation, and anatomy atid physiology, organology and histology, ontogeny and systematic zoology have been advanced to a surprising degree. The investigation of the lower animals has since then been recognized as a wide field of work, whose exploration is of great significance for all branches of science and to which we owe numberless special and the most important general conclusions. The general belief of zoologists regarding the extent of this rich pelagic animal world arose as the result of the discovery that a s])ecial "pelagic fauna" exists, composed of many characteristic forms, funda- mentally different from the littoral fauna. This pelagic fauna is made uj) of animals (some floating passively, others actively swimming) which remain at the surface of the sea and never leave it, or only for a short time descend to a slight dei)th. Among such true "pelagic animals" are the radiolaria, peridinia, noctiluca, medusiie, siphonophores, cten- ophores, sagitta, pteropods, heteropods, a greater.part of the Crustacea, the larvai of echinoderms, of many worms, etc. Important changes Avere first made in the prevailing idea of the "pelagic fauna" by the remarkable discoveries of the epoch-making Challenger expedition (1873-1870). The two leaders of this, Sir Wyville Thompson and Dr. John Murray, did not limit themselves to their chief object, the general physical and biological investigation of the deep sea, but studied with equal care and perseverance the conditions of organic life at the surface of the ocean and in zones of 5G8 REPORT OF COMMISSIONER OF FISH AND FISHERIES. various depths. As the most significant general result Murray, in his "Preliminary Eeport" (187G), says: Everywhere we have found a rich organic life at and below the surface of the ocean. If living individuals are scarce at the surface, below it the tow net commonly discloses numerous forms, oven to a depth of 1,000 fathoms and more (5, p. 536). In 1875, on the journey through theKorth Pacific Ocean (from Japan to the Sandwich Islands), the extremely important fact was established that the i^elagic organisms in oceanic zones of difi'erent depths belong- to different species; fine pelagic nets (or tow nets) " on many occasions were let down even to depths of 500, 1,000, and 2,000 fathoms, and thereby were discovered many swimming organisms which had never been captured hitherto, either at the surface of the ocean or at slight depths (up to 100 fathoms below the surface)" (0, ]). 758). The most characteristic forms of these zones of different depths belong chiefly to the class of the Radiolaria^ especially to the order of the Pluvodaria. Through the investigation of the Challenger radiolaria, which occupied for ten years the greater part of my time and attention, I was led to study anew these conditions of distribution; and I reached the con- viction that the differences discovered by Murray in the pelagic fauna, at different depths of the ocean, were still more significant than he assumed, and that they had the greatest significance, not merely for the radiolaria, but also for other groups of swimming oceanic organisms.